1. Field of the Invention
This invention concerns a hand-operated control system for orienting aircraft. More particularly, it concerns a hand-operated yaw control system for controlling the tail rotor of a helicopter.
2. General Discussion of the Background
A helicopter is supported in hovering flight by rotation of a main rotor blade assembly comprised of two, three or four individual rotor blades. The altitude of the helicopter can be varied by changing the angle of attack of each of the individual blades, an increase in the angle of attack generating more lift while a decrease in the angle of attack generates less lift. Translational movement parallel to the ground is achieved by tilting the entire rotor blade assembly so that the tip plane path of the assembly tilts in the desired direction of horizontal movement.
In addition to the main rotor blade assembly, most helicopters are equipped with a tail rotor having an axis of rotation perpendicular to the rotational axis of the main rotor blade assembly. The purpose of the tail rotor assembly is to counteract the torque induced in the body of the helicopter by rotation of the main rotor assembly. The amount of antitorque force exerted by the tail rotor assembly is controlled by changing the angle of attack of the individual blades which comprise it.
In many conventional helicopters, the angle of attack of each of the main rotor assembly blades is controlled by a collective pitch lever or stick located by the left side of the pilot's seat. This lever is moved up and down by the pilot's left hand, and through a series of mechanical linkages changes the pitch angle of the main rotor blades. As the collective pitch lever is raised, there is a simultaneous and equal increase in the pitch angle of each of the main rotor blades; as the lever is lowered, there is a simultaneous and equal decrease in the pitch angle. The amount of movement of the lever determines the amount of pitch blade change, thereby determining the degree of upward or downward change in altitude.
A cyclic control stick is generally located in front of the pilot's seat so that it is positioned between the legs of the pilot. The purpose of the cyclic control is to tilt the tip-path plane in the direction of desired horizontal movement. The blades of the main rotor assembly are attached to a rotor disc which tilts in the direction that pressure is applied to the cyclic control stick. If the cyclic stick is moved forward, the rotor disc tilts forward; if the cyclic is moved aft, the rotor disc tilts aft, and so on.
The thrust produced by the tail rotor assembly is governed by the position of antitorque pedals located in front of and below the pilot's seat. The pedals are linked to a pitch change mechanism in the tail rotor gear box to permit the pilot to increase or decrease the pitch of the individual tail rotor blades. The changing pitch of these blades exerts a varying force to counteract the torque exerted on the body of the helicopter by rotation of the main rotor assembly. An additional function of the tail rotor assembly is to control heading of the helicopter during hovering flight and hovering turns.
It is a demanding task to pilot a helicopter since the pilot must constantly be operating the variety of control sticks and pedals in the cockpit. A change in altitude, for example, requires an increase in engine RPM, thereby increasing the amount of torque imparted to the helicopter body and requiring application of force to the tail rotor control pedals to counteract the additional torque. Changes in air density at varying altitudes can also affect required rotor RPM, thereby requiring compensating movements of the collective control stick and rotor pedals. Because of the necessity for constant manipulation of the foot pedals in response to changing conditions, it is essential that a helicopter pilot have complete control over these pedal functions if disaster is to be avoided.
One of the hazards of piloting a helicopter, especially in battle conditions, is that the pilot can be wounded and lose control of leg functions. When such an incident occurs, the pilot loses a vital degree of control over the aircraft, and fatal crashes often ensue.
Since helicopters have controls that typically require manipulation with both arms and both legs, paraplegics have also been unable to fly them. Some attempts have been made to develop control systems that eliminate the need for pedal movement, yet none of them have had wide acceptance.
Conventional fixed wing aircraft also have pedals for controlling rudders involved in operation of the aircraft. Although the demands on the pilot are not as constant in a fixed wing aircraft as in a helicopter, there still exists a need for providing aircraft controls that can be operated by someone without the use of his legs or feet.
Although many efforts have been made to provide an aircraft or helicopter that eliminates the need for operation of foot pedals, a truly satisfactory solution has not been found. For example, U.S. Pat. Nos. 1,798,724, 3,350,956, and 4,134,560 all disclose mechanisms for eliminating foot pedal controls in an aircraft. All these mechanisms, however, require extensive modifications to the aircraft itself because the control sticks and pedals are eliminated and their functions incorporated into a single device. The solutions disclosed in these patents have never been widely accepted because of the expense of modifying the basic control systems of the aircraft. Furthermore, such integrated control systems are unsuitable for adapting an already existing helicopter or airplane for use by a paraplegic.
U.S. Pat. No. 4,062,508 concerns a helicopter rotor control mechanism for combining cyclic and collective rotor control functions in a single stick. It does not address the problem of providing tail rotor control without the use of foot pedals.
It is accordingly an object of this invention to eliminate the necessity for using foot pedals in controlling an airplane, helicopter, or other vehicles having a foot-actuated orientation control system.
Another object of the invention is to provide a hand-operated control system for orienting such craft which can be easily installed on existing aircraft without the necessity for extensive modification of the underlying control system.
It is still another object of the invention to provide a redundant, hand-operated control system which can function in tandem with or in place of existing foot pedal controls.
Yet another object is to provide a hand-operated control system that can be mounted on existing hand-operated control sticks without affecting the operation of the existing controls while allowing completely independent operation of the control system and existing hand-operated controls.
Finally, it is an object of this invention to provide such a system that can be economically and quickly installed.